1. Field of the Invention
The present invention relates to a recordable optical recording medium of LTH (Low to High) recording type, having a recording layer that contains organic dye and capable of recording and playing back data using light of 300 nm to 500 nm in wavelength. To be specific, the present invention relates to a recordable optical recording medium of LTH (Low to High) recording type, having a recording layer that contains organic dye and capable of recording and playing back data using light of 300 nm to 500 nm in wavelength, wherein said recordable optical recording medium permits a light transmission layer of one-layer configuration and whose characteristics do not deteriorate when stored in a high-temperature, high-humidity environment.
2. Description of the Related Art
Conventional LTH-type BD-R discs with a recording layer that uses organic dye material have a cover layer of two-layer structure (the number of layers excludes a hardcoat layer). One of these layers is a cover layer made of hard material to resist scratching, as with HTL-type BD-R discs whose recording layer uses inorganic material; while the other layer is a cover layer that uses soft (low in elastic modulus (20 MPa or less)) material (acrylic resin or pressure-sensitive adhesive) for the purpose of accepting deformation caused by heat generation and expansion of dye when recording is conducted, maintaining a deformed state, and ensuring sufficient characteristics with Δnd. To realize low-cost organic BD-Rs, however, it is desirable to have a cover layer of one-layer configuration made of hard material, as with inorganic BD-Rs. An azo metal complex having a specific molecular structure is proposed as an organic dye material for recordable optical recording media having such cover layer of one-layer configuration (Japanese Patent Laid-open No. 2010-33639 and Japanese Patent Laid-open No. 2010-143184). One feature of this dye is that it is subject to less deformation when recording is conducted and consequently achieves a cover layer of one-layer configuration. However, discs which use this dye as a recording layer material and whose reflection layer is made with silver or silver alloy present problems in that their recording characteristics deteriorate as the dye in the recording layer reacts with silver in the reflection layer when exposed to a high-temperature, high-humidity environment, thereby causing the dye to change its properties.